In closed loop water systems and systems in which the water in service may vary due to changes in service demand, the water usually becomes contaminated by both suspended solids and biological growth. For example, in a system which loses water, make up water must be added in order to maintain a given volume of water in the system. However, this process of adding water eventually results in a concentration of dissolved inorganic matter such as metallic salts, e.g., calcium and magnesium. Depending upon the nature of the dissolved salts and the temperature of the solution, these salts can precipitate out as carbonate scale on the interior surfaces of the system. Such scale may occlude or even stop the flow of water through the system. It also causes friction losses and thermal losses at heat transfer surfaces. In addition, the scale functions as a host substance upon which, and inside the crevices of which, algae and/or bacteria can grow. Also, in systems including open bodies of water, e.g. cooling towers, pools, fish hatcheries, etc., circulating water often picks up dirt, bacteria, pollen, stack emissions and other pollutants from the air. The presence and growth of algae and microorganisms are also a problem in systems such as this. Algae can cause plugged water passages. Also, some bacteria produce acids which can attack metal surfaces directly. Other types of bacteria, e.g. nitrifying bacteria, react with dissolved ammonia to produce nitric acid which can attack metal surfaces.
There are a variety of known techniques for minimizing the build up of scale in water systems and for minimizing the growth of organisms such as bacteria and algae. For example, chemical agents have been used to change the nature of the material in the water or to treat surfaces so that the material in the water does not affect the surfaces. These agents include scale inhibitors, wetting agents, algacides, acids, each with its own job to do. However it is difficult to keep all of these chemicals in balance because of changing conditions in the system. Also, such chemicals become a hazard to the environment through blow-down and material handling.
To avoid having to use such chemicals, some water systems incorporate filters in order to remove materials such as scale particles and algae entrained in the circulating water.
It is also known that the growth of algae can be greatly inhibited or prevented by exposing the circulating water to ultraviolet light. Accordingly, in some systems, the water is flowed through one or more radiation chambers bathed in ultraviolet light. However, this procedure has not been entirely satisfactory because the water usually contains an appreciable amount of suspended solids or turbidity which prevents the ultraviolet light emitted by the light source from propagating through the water far enough to kill all the orqanisms entrained in the water before the water passes out of the radiation chamber.
The effectiveness of radiation chambers in removing algae and other biological organisms is also degraded because, as noted above, inorganic material, i.e., dissolved salts, tends to plate out on the warmer surfaces or the system forming scale. Therefore, after the ultraviolet lamps have been in use for only a relatively short period of time, scale forms on the surfaces of the lamps, dramatically reducing the intensity of the radiation from those lamps and greatly reducing their effectiveness in killing biological organisms in the water.
It is also known that an electrostatic field can effect the electrochemical characteristics of the various metallic salts, such as magnesium and calcium, which are the building blocks of scale in all water systems. In fact, some systems incorporate one or more electrostatic probes, each of which projects into the water being circulated and is energized so that an electrostatic field emanates from the probe into the water. The electrostatic field affects the valence of the metallic salts dissolved in the water so that the salts tend to remain in solution.
Also, since the salts are now more easily held in solution, additional salts can be absorbed by the water so that previously deposited scale actually tends to redissolve. Resultantly, the use of such probes may result in scale being removed from internal surfaces of the system over time. It is also been found that such electrostatic fields upset the electrochemical balance of biological components in the water, such as bacteria and algae, so that their reproductive capacities are inhibited.
While each of the aforesaid devices, i.e., filter, ultraviolet light source and electrostatic probe have been used heretofore in diverse water systems to improve the characteristics of the water circulating in those systems, to our knowledge, they have never been organized as described hereinafter so that the three different devices combine, coact and operate in synergism to maximize the effectiveness of each of the devices in the performance of its function thereby to optimize the removal of inorganic and organic contaminants from water circulating in such water systems.